Some of the new PHP 5.3 features, including namespaces and anonymous functions, are not compatible with PHPDocumentor, even with the latest release. For example, it just raises
YUI Doc is language agnostic. It could be used. Here's a video describing its use: http://developer.yahoo.com/yui/theater/video.php?v=woods-yuiconf2009-yuidoc
You could try DocBlox; which is intended to be an alternative for phpDocumentor but with support for additional features of which full PHP 5.3 support is one. An additional benefit is that is it quite fast and uses relatively little memory.
You can read more on http://www.docblox-project.org or see a demo at http://demo.docblox-project.org/default
Check ApiGen API documentation generator with PHP 5.3 support
This was already mentioned in a comment by @mvriel, but I'll make it an answer: phpDocumentor's successor is phpDocumentor 2. From its website:
phpDocumentor 2 is build to generate API documentation for all features available in PHP 5.3 and higher.
phpDocumentor 2 is the result of the merge between phpDocumentor and DocBlox. From the merge announcement in DocBlox's website:
Announcing phpDocumentor 2 – the merging of the old (phpDocumentor) and the new (DocBlox).
...
Old phpDocumentor is retiring. Some bugfix effort may continue into bringing phpDocumentor 1.x to a close, but most effort going forward will be spent on 2.x.
It's still in alpha stage (as of 2013-04-01), but usable.
Well, I've found PHPDoctor, which works pretty well with PHP 5.3. Although, I'd be still interested if anyone found something better, so I'm not closing the question.